1. Field of the Invention
The present invention relates generally to gyro apparatus and, more particularly, is directed to a gyro apparatus of a small size which can be mounted on a ship and also on a land navigation vehicle.
2. Description of the Prior Art
An outline of a prior art gyro apparatus previously proposed by the present applicant of the invention (see, for example, U.S. Pat. No. 3,855,711) will be described briefly with reference to FIGS. 1 to 5.
In FIG. 1, reference numeral 1 designates a gyro casing or housing which incorporates therein a gyro rotor rotating at a high speed and which is formed as a liquid-tight structure. Reference numeral 2 designates a container or receptacle container like a tank which surrounds the gyro casing 1. Reference numeral 3 designates a suspension wire which supports the gyro casing 1. The upper end of the supension wire 3 is fixed to the container 2 and the lower end thereof is fixed to the gyro casing 1. Reference numerals 4N, 4S and 5N, 5S respectively designate primary sides and secondary sides of a non-contact type displacement detecting apparatus 6. The primary sides 4N and 4S are respectively attached on the surface of, for example, the gyro casing 1 at intersections where the extended line of the spin axis of the gyro intersects the surface of the gyro casing 1, that is, the north side and the south side of the gyro. While, the secondary sides 5N and 5S are respectively attached to the container 2 at its positions corresponding to the primary sides 4N and 4S. Reference numeral 7 designates a liquid such as a damping oil or the like having a high viscosity and this liquid 7 is filled into the container 2. At the positions (east and west) on the equator of the container 2 and perpendicular to the spin axis, there are attached one ends of a pair of horizontal axes 8 and 8', while the other ends thereof are rotatably engaged with bearings 13 and 13' which are provided at the corresponding positions of a horizontal ring 12. Reference numeral 10 designates a horizontal follow-up servo motor and which is attached to the horizontal ring 12. A horizontal gear 9 is attached to one horizontal shaft 8 and this horizontal gear 9 is engaged with a horizontal pinion 11 which is mounted to the rotary shaft of the servo motor 10. Gimbal shafts 14 and 14' are respectively attached to the horizontal ring 12 at its positions perpendicular to the afore-mentioned horizontal shaft bearings 13 and 13'. These gimbal shafts 14 and 14' are rotatably engaged with gimbal shaft bearings 15 and 15' which are attached to a follow-up ring 16 at corresponding positions, respectively. To the upper end and the lower end of the follow-up ring 16, there are attached follow-up shafts 17 and 17' the free ends of which are rotatably engaged with follow-up shaft bearings 25 and 25' mounted on a binnacle 24 at its corresponding positions. An azimuth gear 21 is attached to one follow-up shaft 17. Reference numeral 19 designates an azimuth follow-up servo motor mounted on the binnacle 24 and reference numeral 20 designate an azimuth pinion attached to the rotary shaft of the azimuth follow-up servo motor 19. This azimuth pinion 20 is engaged with an azimuth gear 21. Reference numeral 22 designates a compass card which is attached to the follow-up shaft 17'. Reference numeral 23 designates a base line plate attached on the upper surface of the binnacle 24 so as to oppose to the compass card 22. By a base line 26 drawn on the central portion of the base line plate 23 and the compass card 22, it is possible to read the course of the navigation vehicle which is equipped with this gyro apparatus.
Subsequently, one practical example of the above mentioned non-contact type displacement detecting apparatus 6 used in this prior art gyro apparatus will be described with reference to FIGS. 2 and 3. FIG. 2 shows one set at the N (north) side thereof. As shown in FIG. 2, the primary side (4N) is made as one primary winding, in which the winding wire is located within the plane perpendicular to the spin axis of the gyro rotor and is generally excited by an alternate current which is used commonly by a gyro current source to thereby form alternate magnetic fields shown by broken line arrows a1 and a1'. Similarly, the secondary side (5N) is formed of 4 rectangular windings 5NW, 5NE, 5NU and 5NL, in which the pair of windings 5NW and 5NE are located in parallel to each other in the lateral direction, while another pair of the windings 5NU and 5NL are located in the up and down direction. The winding starting ends of the pair of the windings 5NW and 5NE and the winding starting ends of the pair of the windings 5NU and 5NL are connected to one another. Let it now be considered that the primary winding 4N, that is, the gyro casing 1 be positioned at the center of the secondary winding 5N, that is, the container 2. Then, since the magnetic flux generated by the primary winding 4N penetrates each of 4 secondary windings 5NW, 5NE, 5NU and 5NL, voltages are induced at the respective 4 windings 5NW, 5NE, 5NU and 5NL in response to the voltages. However, since the changes of the magnetic flux in each of the four secondary windings 5NW, 5NE, 5NU and 5NL are substantially the same and also the respective pairs of the windings are connected in a differential fashion as described above, no voltage is generated at their output terminals 2-1 and 2-2 at all. When the primary winding 4N, is deviated in, for example, the east (shown by E in FIG. 2), the magnetic flux penetrating the secondary winding 5NE is increased while the magnetic flux penetrating the secondary winding 5NW is decreased. As a result, although the voltage is generated at the output terminal 2-1, no voltage is generated at the output terminal 2-2.
On the other hand, when the primary winding 4N is deviated in the west (shown by W in FIG. 2), contrary to the above, the induced voltage of the secondary winding 5NW is increased and the induced voltage of the secondary winding 5NE is decreased so that a voltage having a phase opposite to that of the case where the primary winding 4N is deviated in the east is generated at the terminal 2-1. In this case, since the secondary windings 5NU and 5NL are located in the up and down direction, no output voltage is generated at the output terminal 2-2 similary as described above. Whereas, when the primary winding 4N is displaced in the up and down direction, although no output voltage is generated at the secondary windings 5NW and 5NE which are located in the lateral direction, the voltage is generated at the secondary windings 5NL and 5NU located in the vertical direction so that the output voltage is generated at the terminal 2-2. In other words, according to the gyro apparatus having the structure shown in FIG. 1, it is possible to detect the displacement of the gyro casing 1 at the N end in the east-and-west direction and the up-and-down direction relative to the container 2.
FIG. 3 shows only the detecting apparatus which detects the displacement in the east-and-west direction and FIG. 3 is a location diagram showing the gyro casing 1 from the top thereof. Specifically, the displacement detecting apparatus at the S side is formed of a primary winding 4S and secondary windings 5SE and 5SW. When the gyro casing 1 is deviated in the east, the magnetic flux passing through the secondary winding 5SE is increased, while the magnetic field passing through the secondary winding 5SW is decreased so that a voltage is induced in the terminal 3-1. The phase of this voltage is selected to be the same as that of the voltage developed at the terminal 2-1 of the secondary windings 5NW and 5NE. Further, as shown in FIG. 3, the secondary windings 5SE, 5SW and 5NE, 5NW are further connected in a differential fashion so that when the gyro casing 1 is displaced in the east-and-west direction, no voltage is developed at a terminal 3-2, while when the gyro casing 1 generates an angular displacement around a vertical axis line O (vertical to the sheet of drawing), an output voltage having a phase inverted by 180.degree. is generated at the terminal 3-2 in response to the rotation direction of the gyro casing 1.
This output voltage from the terminal 3-2 is supplied through a servo amplifier 30 (or may be supplied directly) to the control winding of the azimuth servo motor 19. The rotation of the aziumth servo motor 19 is transmitted through the azimuth pinion 20, the azimuth gear 21, the follow-up ring 16 and the horizontal ring 12 to the container 2, whereby this container 2 is controlled such that the angular displacement thereof around the above described vertical axis line becomes zero. In other words, whatever direction the gyro casing 1 is displaced in, the suspension wire 3 can be perfectly prevented from being twisted by this servo system. Thus, the gyro apparatus can be protected from the application of an external disturbance with respect to its vertical axis. In FIG. 3, reference numeral 3-3 designates an error correction signal generating apparatus which generates a voltage corresponding to the speed of the ship or its latitude, displaces the follow-up operation of the azimuth follow-up system to thereby twist the suspension wire 3 and applies a torque around the vertical axis of the gyro apparatus to thereby correct the error.
FIG. 4 shows the horizontal follow-up system, in which the windings 5NU, 5NL and 5SU and 5SL of the secondary sides 5N and 5S are connected in a differential fashion similarly as described above. Accordingly, no output voltage is generated at a terminal 4-1 of the secondary windings 5NU and 5NL when the gyro casing 1 is moved in parallel to the container 2 in the up and down direction, while a voltage is generated at the terminal 4-1 relative to the angular movement around the horizontal axis. This output voltage is supplied through a servo amplifier 31 (or may be supplied directly) to the control winding of the horizontal follow-up servo motor 10. The rotation of the horizontal follow-up servo motor 10 is transmitted through the horizontal pinion 11 and the horizontal gear 9 to the container 2 and thereby the container 2 is rotated. Thus, the above described angular displacement of the container 2 is made zero.
FIG. 5 schematically illustrates the inside of the container 2. In this case, the north-seeking end (A) side (existing on the gyro casing 1) extended from the spin axis of the gyro rotor GR within the gyro casing 1 is inclined upwardly by an angle .theta. relative to the horizontal plane H--H'. Here, O.sub.1 assumes the center of gravity of the gyro casing 1, Q assumes the connection point of the suspension wire 3 and the gyro casing 1, P assumes the connection point of the suspension wire 3 and the container 2 and O.sub.2 assumes the center of the container 2. Further, let it be assumed that when the spin axis of the gyro rotor GR within the gyro casing 1 is horizontal (.theta.=0), the center of graity O.sub.1 of that the gyro casing 1 is coincident with the center of the container 2. Furthermore, A assumes the north-seeking end, B assumes points spaced apart by 180.degree. on the gyro casing 1 and A' and B' respectively assume points on the container 2 and which are corresponding to the points A and B.
Since the suspension wire 3 has a flexural rigidity in practice, it presents a flexed curve as shown by a broken line in FIG. 5. Accordingly, it is appreciated that the axis direction moving amount .xi. (O.sub.2 to O.sub.1) of the gyro casing 1 relative to the container 2 be reduced very slightly. However, in the practical design, this influence is very small so that the description will be made under the assumption that the suspension wire 3 be perfectly flexible. Since the points A' and B' on the container 2 and the points A and B on the gyro casing 1 are arranged by the action of the servo system so as to always exist on the same straight line as mentioned before, the container 2 is also inclined by the angle .theta. relative to the horizontal plane H--H' similarly to the gyro casing 1. Now, let it be assumed that no external acceleration be applied to the gyro apparatus. Then, since no external force is applied to the gyro casing 1 in spin axis direction of the gyro rotor GR, the suspension wire 3 coincides with the vertical line. If the tension of the suspension wire 3 is taken as T and the residual mass of the gyro casing 1 except the bouyancy applied thereto by the damping liquid 7 is taken as mg, the tension T of the suspension wire 3 generates around the point O.sub.1 a moment M expressed as EQU M=Tr sin.theta.=mg r sin.theta.
This moment M is applied to the gyro as the torque around the horizontal axis (which passes through the point O.sub.1 and is perpendicular to the sheet of drawing). In the above equation, reference letter r designates a distance between the center of gravity O.sub.1 of the gyro casing 1 and the connection point Q of the suspension wire 3 and the gyro casing 1 as shown in FIG. 5. In other words, according to this method, it is possible to "apply the torque proportional to the inclination of the spin axis relative to the horizontal plane to the gyro around its horizontal axis". Therefore, if the cycle or the period of the north-seeking movement of the gyro is determined in a range from several 10s minutes to one hundred and several 10s minutes by selecting the distance r, the residual mass mg and the angular momentum of the gyro, it becomes possible to obtain a gyro compass.
However, if the above mentioned gyro compass is further miniaturized so as to be mounted on a smaller navigation vehicle, there occurs drastic difficulty. The first difficulty is that the gyro compass is strongly required to be high in precision. Generally, in the gyro apparatus such as gyro compass and the like, the property of the gyro apparatus is substantially determined by the ratio between the disturbing torque and the angular momentum of the gyro, that is, the drift rate of the gyro. To miniaturize the gyro apparatus means that the dimension of the outer diameter of the gyro rotor must be reduced necessarily. In this case, since the angular momentum of the gyro rotor is in proportional to the fourth power of the outer diameter of the gyro, if the disturbing torque is constant, to miniaturize the gyro apparatus means the rapid increase of the drift rate of the gyro. As a result, it becomes impossible to satisfy the system property of the gyro apparatus.
The second difficulty is caused by the structure of the gyro, particularly the structures and arrangements of the gimbal, the servo motor, the slip ring, the bearing and so on. If the assembly and the arrangement thereof and so on are not taken into a deliberate consideration, it is yet very difficult to miniaturize the gyro compass.